I've used the price promise on many occasions, generally when I purchase a ticket on BA.com and get landed with the horrid Credit Card charge. I then hot foot over to www.americanairlines.co.uk and price up the itin. Generally if availability still exists I put in a claim and get the Credit Card charge back.

Has worked like a charm every time, although be warned, you can only make one claim a day so if you book a return trip as two singles you can only claim for one (unless you book on different days).

I know the charge is only a few quid, but I begrudge paying it when other sites offer the payments on credit cards for free and tried once to see if they'd refund it, and was pleasantly surprised when they did!